1. Field of the Invention
The present invention relates to ignition timing control methods and systems therefor in an engine, and particularly to improvements in an ignition timing control method and a system therefor suitable for a spark ignition engine (hereinafter referred to as an "engine") mounted on a motor car, wherein ignition timing can be constantly controlled to the optimum condition in accordance with the operating conditions of the engine.
2. Description of the Prior Art
In general, ignition timing of an engine has a considerable influence on the output, fuel consumption performance and the like of the engine. Consequently, heretofore, the ignition timing of the engines has been controlled such that the operating conditions of the engine, such as the number of rotation, intake negative pressure and the like, are detected so as to effect the ignition at the preset optimum ignition timing in accordance to the values thus detected. Furthermore, as for other control factors, such as an exhaust gas recirculation rate, cooling water temperature and the like, the ignition timing is changed in accordance with the values of those control factors to correct the ignition timing to the optimum. However, according to the abovedescribed method, influences from the atmospheric pressure, ambient temperature, humidity and the like cannot be corrected, and moreover, a multiplicity of sensors are required to detect all of the factors for correction. Further, even factors not readily detectable, such as aging of the engine due to mechanical wear, variation in fuel quality and the like vary the optimum ignition timing required, and, for those factors, control to the optimum ignition timing has been difficult by the conventional ignition timing control method. Consequently, it has been the common practice to be prepared for losses in fuel consumption and output of the engine for disturbances uncontrollable. For example, FIG. 1 shows the relationship between the humidity and the optimum ignition timing, in which, depending on the ambient conditions when the engine is used, the optimum ignition timing has varied through 7.degree. to 8.degree. by a crank angle, thus resulting in deteriorated performance to a considerable extent. Furthermore, as for the variation in ignition timing due to the aging with time and the like, it has been expected that the optimum ignition timing is variable through 15.degree. to 20.degree. by the crank angle at the largest to the ignition timing preset in accordance with the initial operating condition of the engine and the standard atmospheric condition, thus resulting in 10 to 20% of fuel consumption loss. However, heretofore, this loss could not be decreased or eliminated.
On the other hand, as described in U.S. Pat. No. 3,142,967, such an invention analogous to the present invention has been proposed that the fluctuations in torque are detected from an output of an alternator or an acceleration of the rotation of the engine to thereby feedback control the ignition timing. However, this proposal presents such disadvantages that a complicated arrangement is required for a sensor for detecting the torque fluctuations from the alternator or an output shaft of the engine, and reliability is low.